When a denture is used for a long period of time, the fitness becomes worse due to absorption of the residual ridge and to the change in occlusion, leading to reduction in their retention and stability. And when an unfit denture is used as it is, since a non-uniform occlusal stress is applied to a mucosa below the denture base, a pain may be caused, and an uleur and inflammation are likely generated. For these reasons, it is necessary to recover the fitness of a denture by repair or reproduction of the denture. In the actual clinics, these treatments are carried out by undergoing lining of a soft material called as a tissue conditioner on the mucosal surface of the denture base to improve the mucosa below the denture base. The tissue conditioner which is used at this time is generally composed of a powder comprising a methacrylic ester-based polymer and a liquid containing, as a major component, a plasticizer such as phthalic esters, and these materials are used upon mixing at the time of use. The tissue conditioner must be frequently exchanged at intervals between several days and one week while examining the degree of improvement of the oral mucosa, and such an operation was extremely difficult. Although the tissue conditioner is usually peeled off by means of fingers or a carving knife, or the like, since not only the tissue conditioner is well adhered to the denture, but also the tensile strength of this material is low, it was likely torn off and left on the denture. While the tissue conditioner remained on and adhered to the surface of the denture base is cut off by means of a grinding bur or the like, since this material is a very soft material, it was extremely difficult to completely remove it.
In order to solve these problems, the present inventors made extensive investigations with respect to a separating material for tissue conditioners. Though this separating material can firmly fix a tissue conditioner to a denture during the use, it must be readily peeled off from the denture after the use. In each of the dental fields, vaseline is widely used as the separating material. While the present inventors investigated the use of vaseline as a separating material at the beginning, it was found that this material has the following drawbacks as the separating material.
(1) In the long-term water immersion test at 37.degree. C. on the assumption of the inside of the oral cavity, the separating effect decreases with a lapse of time.
(2) The viscosity is so high that it is difficult to uniformly apply it to the denture. For this reason, the applied surface is likely uneven so that the separability is too good, whereby the tissue conditioner may be dropped from the denture, or it is applied too thin so that no separability may be shown at all.
In the general industrial field, silicone oil is widely used as a separating material. According to experiments made by the present inventors, this did not substantially show a separating effect as a tissue conditioner.
The tissue conditioner contains even 40% by weight of a plasticizer as one of the essential components thereof. Since plasticizers are very compatible with polymeric materials, the plasticizer contained in the tissue conditioner penetrates into silicone oil or vaseline, or is mixed with them, whereby it possibly reaches the denture. Once the tissue conditioner is brought into contact with a methacrylic resin-made denture, since the plasticizer also penetrates into the denture, it can be easily expected that the adhesive force increases with a lapse of time. For this reason, the present inventors considered that one which can form a firm coating film on the denture surface is effective as the separating material.
As one method, if an appropriate polymer is dissolved in an organic solvent and applied to the denture surface, a firm coating film can be formed. However, a methacrylic resin which is a typical material for dentures generates dry spots, cracks and the like due to the presence of organic solvents such as ethanol, acetone, dichloromethane, and toluene. For this reason, even when a polymer having a separating effect is found out, it is extremely difficult to find out a solvent for this polymer, which does not denature the methacrylic resin-made denture. Moreover, the use of these organic solvents in the room is not desired from the standpoints of their inherent malodors, toxicity and inflammability, and the like. With such backgrounds in mind, the present inventors reached the conclusion that one which forms a firm coating film after the application but does not contain an organic solvent as a major component is useful as the denture base separating material.